Characterizing the 700 km wide system of active faults on the Shan Plateau, southeast of the eastern Himalayan syntaxis, is critical to understanding the geodynamics and seismic hazard of the large region that straddles neighboring China, Myanmar, Thailand, Laos, and Vietnam. Here we evaluate the fault styles and slip rates over multi‐timescales, reanalyze previously published short‐term Global Positioning System (GPS) velocities, and evaluate slip‐rate gradients to interpret the regional kinematics and geodynamics that drive the crustal motion. Relative to the Sunda plate, GPS velocities across the Shan Plateau define a broad arcuate tongue‐like crustal motion with a progressively northwestward increase in sinistral shear over a distance of ~700 km followed by a decrease over the final ~100 km to the syntaxis. The cumulative GPS slip rate across the entire sinistral‐slip fault system on the Shan Plateau is ~12 mm/year. Our observations of the fault geometry, slip rates, and arcuate southwesterly directed tongue‐like patterns of GPS velocities across the region suggest that the fault kinematics is characterized by a regional southwestward distributed shear across the Shan Plateau, compared to more block‐like rotation and indentation north of the Red River fault. The fault geometry, kinematics, and regional GPS velocities are difficult to reconcile with regional bookshelf faulting between the Red River and Sagaing faults or localized lower crustal channel flows beneath this region. The crustal motion and fault kinematics can be driven by a combination of basal traction of a clockwise, southwestward asthenospheric flow around the eastern Himalayan syntaxis and gravitation or shear‐driven indentation from north of the Shan Plateau.

Continental‐scale shear zones play an important role in accommodating block extrusion and rotation as shown by deformation on the Ailaoshan‐Red River shear zone (ASRRSZ) in the SE Tibetan Plateau. This study presents 13 apatite (U‐Th)/He, 11 zircon (U‐Th)/He, and three apatite fission track dates, together with thermal modeling in the Ailaoshan and Xuelongshan segments (ALSZ and XLSZ) of the shear zone to investigate its Cenozoic exhumation history and mechanism, which are critical for understanding its tectonic and landscape evolution. Our results, combined with published chronologic data, reveal that shear zone rocks along the ALSZ experienced prominent and rapid cooling from high temperature (>500°C) to 120–60°C at a rate of 75–100°C/Myr during 29–17 Ma with northwestward younging onset. A second, lower magnitude accelerated cooling occurred at 14–10 Ma along the ALSZ at a rate of 20–30°C/Myr, with a later initiation on the XLSZ at ~5 Ma and continuing to present with a cooling rate of ~20°C/Myr. Thermal modeling reveals a single rapid cooling phase with a rate of 17–14°C/Myr in the Eocene to early Oligocene for samples outside the shear zones. These three fast cooling episodes are directly related to deformation stages including crustal shortening across the SE plateau, sinistral ductile shearing along the ASRRSZ, and dextral faulting with a dip‐slip component on the Red River and Weixi‐Qiaohou faults along the shear zone flanks. Furthermore, the northward migration of kinematic reversal and associated cooling along strike since the mid‐late Miocene likely reflects the northward advance of the eastern Himalayan syntaxis.

This work was supported by a National Science Foundation grant from the Tectonics program (EAR-0911587) to E.K. and K.P.F. Additional support to E.W. was provided by grants from the Chinese Academy of Sciences (XDB03010500). X.S. also thanks the support from the Earth Observatory of Singapore, Nanyang Technological University through its funding from the National Research Foundation Singapore and the Singapore Ministry of Education under the Research Centers of Excellence initiative.Variations in the strength of the Asian monsoon during Holocene time are thought to have been associated with widespread changes in precipitation across much of Tibet. Local records of monsoon strength from cave deposits, ice cores, and lake sediments typically rely on proxy data that relate isotopic variations to changes in precipitation. Lake expansion and contraction in response to changing water balance are likewise inferred from sedimentologic, isotopic and paleobiologic proxies, but relatively few direct records of changes in lake volume from preserved shorelines exist. Here we utilize relict shoreline deposits and associated alluvial fan features around Siling Co, the largest lake in central Tibet, to reconstruct centennial-to-millennial-scale variations in lake area and volume over the Holocene. Mapping and surveying of lacustrine shorelines coupled with optically stimulated luminescence dating of associated deposits indicate protracted occupation of a highstand elevation from >8 ka to 4 ka, followed by rapid recession that was likely punctuated by several stillstands of centennial-scale duration. Calculation of the changes in lake surface area and past hydrologic indices of the Siling Co basin suggests the effective moisture during the early Holocene highstand was approximately three times greater than today. In contrast to other lakes in central and western Tibet, our results suggest that Siling Co did not begin to recede synchronously with decreasing solar insolation at ca. 9–8 ka. Rather, initial recession of Siling Co appears to correspond to a time period of enhanced aridity and weakened monsoon in both Africa and Asia at ca. 4.2 ka. Our results add to a growing body of literature that suggest a period of relatively severe aridity on the Tibetan Plateau at this time. We suggest that subsequent punctuated recession of Siling Co was punctuated by similar periods of abrupt climate change during the Late Holocene.Publisher PDFPeer reviewe

The Red River fault is an important plate‐boundary fault that has played a significant role in the tectonic evolution of northern Southeast Asia. Nonetheless, its millennial slip rate and earthquake recurrence behavior are poorly constrained. Analysis of 5‐ and 30‐m‐resolution topography reveals right‐lateral offsets that range from 60 m to 24 km along its “mid‐valley” trace but none along its “range‐front” trace. This strongly implies that the range‐front fault has experienced very little lateral slip for millions of years, even though it is the geologically more significant fault. Stratigraphic and geomorphologic investigation of the mid‐valley fault within a small channel near Gasa yields a¹⁴C‐based slip rate of 1.1 ± 0.4 mm/year, averaged over the last 30,000–50,000 years. Three‐dimensional paleoseismic excavation of colluvial wedges produced by collapse of shutter ridges into the channel shows that sudden dextral ruptures of the fault have occurred every 6,000 ± 1,000 years over the past 30,000 years. Two and possibly three large surface ruptures occurred in the past 13,500 years, and two previous ones occurred at 18,500 and 24,500 calendar years before present (cal yr BP). The oldest one in the section likely occurred at or a few 1,000 years before 29,800 ± 2,000 cal yr BP. The 3‐D extent of the colluvial wedges implies dextral offsets of ≥4.5 m, amounts that are consistent with the slip rate and recurrence interval. The evidence for low slip rate and rare large seismic events is consistent with the lack of large historical earthquakes along the fault and the low Global Positioning System (GPS)‐derived slip rate, but is much lower than widely cited geological slip rates.